Flexible mem= parameter

Flexible mem= parameter

[Jan Engelhardt]

Hello,


mem= can be used to limit the amount of physical memory Linux uses. I 
presume that when specifying mem=256M only the memory from 0x0 to 
0x10000000 is used. Is there a way to tune mem= so that it will use
0x70000000 to 0x80000000? (A compile-time change would suffice.)


Background: I am trying to track down a nondeterministic (but 
reproducible) segfault while building big projects like gcc or glibc. I do 
not think it's a memory problem since it only showed up since I changed to 
gcc 4.1.0 and tweaked it to use -mcpu=ultrasparc (rather than -mcpu=v7) by 
default. I had been building gcc4 before with gcc3 a number of times w/o 
problems. I did ran a userspace memtester for approx 20 hours (`memtest` 
from debian).


Jan Engelhardt
-- 

Re: Flexible mem= parameter

[Randy.Dunlap]

On Fri, 14 Apr 2006 00:49:12 +0200 (MEST) Jan Engelhardt wrote:

> Hello,
> 
> mem= can be used to limit the amount of physical memory Linux uses. I 
> presume that when specifying mem=256M only the memory from 0x0 to 
> 0x10000000 is used. Is there a way to tune mem= so that it will use
> 0x70000000 to 0x80000000? (A compile-time change would suffice.)
> 
> 
> Background: I am trying to track down a nondeterministic (but 
> reproducible) segfault while building big projects like gcc or glibc. I do 
> not think it's a memory problem since it only showed up since I changed to 
> gcc 4.1.0 and tweaked it to use -mcpu=ultrasparc (rather than -mcpu=v7) by 
> default. I had been building gcc4 before with gcc3 a number of times w/o 
> problems. I did ran a userspace memtester for approx 20 hours (`memtest` 
> from debian).

I've never tried it, but Documentation/kernel-parameters.txt
suggests using mem= along with memmap= to specify an exact memmap.

	memmap=nn[KMG]@ss[KMG]
			[KNL] Force usage of a specific region of memory
			Region of memory to be used, from ss to ss+nn.


Is this on a sparc system or are you just building sparc tools?
I don't know if memmap= works on sparc arch.

---
~Randy

Re: Flexible mem= parameter

[Denis Vlasenko]

On Friday 14 April 2006 01:49, Jan Engelhardt wrote:
> Hello,
> 
> 
> mem= can be used to limit the amount of physical memory Linux uses. I 
> presume that when specifying mem=256M only the memory from 0x0 to 
> 0x10000000 is used. Is there a way to tune mem= so that it will use
> 0x70000000 to 0x80000000? (A compile-time change would suffice.)

On i386 this works:

"mem=exactmap mem=640K@0 mem=79M@1M"

> Background: I am trying to track down a nondeterministic (but 
> reproducible) segfault while building big projects like gcc or glibc. I do 
> not think it's a memory problem since it only showed up since I changed to 
> gcc 4.1.0 and tweaked it to use -mcpu=ultrasparc (rather than -mcpu=v7) by 
> default. I had been building gcc4 before with gcc3 a number of times w/o 
> problems. I did ran a userspace memtester for approx 20 hours (`memtest` 
> from debian).
--
vda